For a liquid crystal display apparatus including: a liquid crystal panel that modulates a light beam from a light source according to a video signal; and a backlight unit to illuminate the liquid crystal panel, a technique is known according to which the emission luminance of the light source for the backlight is adapted to be controlled corresponding to the brightness around the liquid crystal display apparatus. In this case, the liquid crystal display apparatus includes a brightness sensor to detect the surrounding brightness, and the emission luminance of the backlight light source is controlled according to the brightness around the liquid crystal display apparatus detected by the brightness sensor. In this case, a visibility that can not be overwhelmed by the surrounding light can be obtained by, for example, brightening the emission luminance of the backlight light source following the brightness around the liquid crystal display when the surround becomes brighter.
In the description hereinafter, “contrast” refers to the difference in the brightness between the darkest portion and brightest portion in an image and “contrast feeling” refers to a vivid impression felt due to the difference in the brightness between the darkest portion and brightest portion in an image.
As to the above technique of controlling the display condition of a screen corresponding to the brightness around a display apparatus, for example, Patent Document 1 discloses an image display device that improves the visibility by increasing the brightness of an image thereon as suppressing the increase of the power consumption. According to this technique, the emission luminance of a backlight is adapted to be controlled using: a white display pixel number calculating portion that calculates the number of white display pixels using an image signal; an surrounding environment brightness detecting portion that detects the brightness of the surrounding environment; the number of white display pixel or the white display area that the above white display pixel number calculating portion has calculated; and the brightness of the surrounding environment that the above surrounding environment luminance detecting portion has detected.
The image display device of the above Patent Document 1 is adapted to provide images each having an excellent contrast suppressing the black portions therein to be lighted and, simultaneously, facilitate suppression of increase of the power consumption, by having stored in a data storing portion experimental data of the surrounding environment luminance and the emission intensity of the backlight obtained to the extent that black portions are not lighted.
The above image display device is provided with the surrounding environment brightness detecting portion that is a sensor capable of always monitoring the brightness of the surrounding environment (the surrounding environment brightness) and this portion controls the emission intensity of the backlight when all pixel display white and, simultaneously, controls the emission intensity of the backlight according to the magnitude of the image luminance. In this case, for a low-brightness display screen on which a small number of pixels display white, the entire screen is brightened by increasing the emission intensity of the backlight to the extent that the black level is not lighted. In contrast, for a bright screen on which a large number of pixels display white, power consumption saving can be facilitated and, simultaneously, a high-brightness display screen is retained by reducing the emission intensity of the backlight to a proper level. The emission intensity of the backlight is controlled using a method of controlling at least one of the backlight current, the emission pulse width (pulse duty), and the number of emission pulses.
For example, Patent Document 2 discloses a liquid crystal display apparatus that is adapted to execute a backlight control based on brightness information of a video, and brightness information around the liquid crystal panel. In this case, the liquid crystal display apparatus includes: a brightness detector to detect the brightness around the liquid crystal panel; and a means that executes the brightness control of the backlight based on the brightness around the liquid crystal panel detected by the brightness detector. For example, when the brightness around the liquid crystal panel becomes lower than a reference value, a dark video looks brighter than usual and, therefore, an inverter power circuit is controlled to reduce the brightness of the backlight (cold cathode tube). In contrast, when the brightness around the liquid crystal panel becomes higher than a reference value, a bright video looks darker than usual and, therefore, the inverter power circuit is controlled to increase the brightness of the backlight (cold cathode tube).
For example, Patent Document 3 discloses a projection type display device that adjusts the illuminance light quantity based on video information and optimally sets the range within which the light quantity adjusting is allowed (light attenuation range) thereof corresponding to the brightness of the viewing environment. In this case, the projection type display device includes a brightness detecting means of detecting the brightness of the viewing environment, and a means of setting the range within which the light quantity of the light source is attenuated based on the brightness of the viewing environment detected by the brightness detecting means. The attenuation light quantity of the light source is increased when the surround is bright, and the attenuation light quantity is reduced when the surround is dark and, thereby, the problem of under-brightness caused by excessive light quantity adjusting can be solved.    Patent Document 1: Japanese Laid-open Patent Publication No. 2004-294767    Patent Document 2: Japanese Laid-Open Patent Publication No. 2001-350134    Patent Document 3: Japanese Laid-Open Patent Publication No. 2004-354882